sse-starlette doesn't respect uvicorn timeout_graceful_shutdown

[BrendanGraham14]

Issue

sse-starlette doesn't seem to respect uvicorn.server.Server.config.timeout_graceful_shutdown.

From some digging, my understanding of the issue is as follows:

• sse_starlette monkey patches uvicorn's signal handler
  • This configures a class called AppStatus, which holds an event should_exit_event
  • The monkey patched signal handler sets should_exit_event
• When EventSourceResponse gets __call__ed, it creates an anyio task group with three tasks:
  1. Stream the response
  2. Ping on the connection every 15s (to avoid a behavior where proxies sometimes auto disconnect after some period of inactivity)
  3. Wait for should_exit_event to be set
• If any of these three tasks exit (i.e. streaming the response finishes, pinging fails, the exit signal handler is triggered), all three tasks get immediately canceled.

The problem is specifically that if should_exit_event is set, then the tasks are immediately canceled without respecting uvicorn.server.Server.config.timeout_graceful_shutdown.

Possible solutions

• Add some asyncio.sleep in AppStatus.handle_exit and possibly a similar force_exit mechanism to Uvicorn to handle receiving multiple signals

[sysid]

@BrendanGraham14 , thank you very much for pointing this out and creating a PR ! Let's continue the discussion there.

[sysid]

See PR comments.